1. Field of the Invention
The invention relates generally to a tire tread. More specifically, this invention relates to tire treads having variable surface area.
2. Description of the Related Art
Tire treads generally extend about the outer circumference of a tire to operate as the intermediary between the tire and a surface upon which it travels (the operating surface). Contact between the tire tread and the operating surface occurs along a footprint of the tire. Tire treads provide grip to resist tire slip that may result during tire acceleration, braking, and/or cornering. Tire treads may also include tread elements, such as ribs or lugs, and tread features, such as grooves and sipes, each of which may assist in providing target tire performance when a tire is operating under particular conditions.
One common problem faced by tire manufacturers is how to extend the life of a tire tread. One solution is to increase the tread thickness; however, increasing tread thickness (i.e., depth) generally increases heat generation and rolling resistance. Therefore, it may be desirous to reduce the thickness of a tire tread to improve tread stiffness, and, consequently, improve the tire's rolling resistance and tread operating temperature. This may then allow the use of improved tread compounds having an improved wear rate, which may comprise, for example, SBR or other high hysteresis compounds, even though the improved compound may otherwise increase tread operating temperatures and/or rolling resistance. This is because lowering the tread thickness may reduce or negate the effects of the high hysteresis tread compound.
Another common problem faced by tire manufacturers is how to maintain and/or improve tire performance during the life of a tire. For example, it may be desired to maintain and/or improve tire performance in wet and/or off-road conditions as the tread wears. Tires commonly used in wet and/or off-road tire conditions generally include treads having surface and volumetric voids. In an attempt to maintain or improve wet and/or off-road performance in worn tread stages, the existing surface voids and volumetric voids may be increased in size to provide additional void for the worn tire tread, or additional surface features added to increase the void. However, these alternations may increase the surface and/or volumetric void in the initial or early stages of the tire beyond that which is desired, and/or the tread becomes less stiff, each of which may negatively affect tire performance. Therefore, there is a need for a tire tread that provides increased void performance at worn stages, especially in the central or intermediate portions of the tread width, without sacrificing tire performance.